Static Electricity

• Static electricity is all about charges which are not free to move, e.g. in insulating materials. This causes them to build up in one place and it often ends with a spark when they do finally move
• Build-up of static is caused by friction
• When certain insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on another. This wil leave the materials electrically charged, with a static charge on one and an equal negative static charge on the other
• Which way the electrons are transferred depends on the 2 materials involved
• The classic examples are polythene and acetate rods being rubbed with a cloth duster

  
• In static electricity only electrons move - never positive charges
• Both +ve and -ve electrostatic charges are only ever produced by the movement of electrons. The positive charges definitely do not move
• A positive static charge is always caused by electrons moving away elsewhere. The material that loses the electrons loses some negative charge, and is left with an equal positive charge
• Too much static causes sparks
• As electric charge build on an object, the potential difference between the object and the earth (which is at 0 V) increases
• If the potential difference gets large enough, electrons can jump across the gap between the charged object and the earth - this is the spark
• Sparks can also jump to any earthed conductor that is nearby - which is why you can get static shocks getting out of a car. A charge builds up on the car's metal frame, and when you touch the car, the charge travels through you to earth
• Sparks usually jump when the gap is fairly small. But not always - lightning is just a really big spark
• Like charges repel, opposite charged attract
• When two electrically charged objects are brought close together they exert a force on one another
• 2 things with opposite electric charges are attracted to each other, while 2 things with the same electric charge will repel each other. These forces get weaker the further apart the 2 things are
• Same and opposite charged forces will cause the objects to more if they're able to do so. This is known as electrostatic attraction / repulsion and is a non-contact force
• One way to see this force is to suspend a rod with a known charge from a piece of string (so it's free to move). Placing an object with the same charge nearby will repel the rod - the rod will move away from the object. An oppositely charged object will cause the rod to move towards the object